Not many airframe-mounted ELTs have worked in helo accidents in Oz for a variety of reasons from improper mounting to the airframe burning.
My suggestion is that if you can afford it, both is the best way. The hand held should be worn (working on the idea of removing as you leave the airframe has severe shortcomings, especially over water) and the airframe model should be multi-axis and serviced regularly. 406 is the way to go also, especially in the more remote areas.